Interdisciplinary Urban Development Sociology of Municipal Street Trading License Fee Schedules and Vendor Cart Mobility Constraints in Nairobi's Central Corridor: A Regression Discontinuity Analysis of Fee Tiers

Municipal street trading license fee schedules in Nairobi's central corridor create discrete fee tiers that may constrain vendor cart mobility, yet the causal effect of crossing a tier boundary cannot be estimated from the observational data typically available to city authorities. the present analysis evaluates whether a regression discontinuity design (RDD) can credibly identify the effect of fee-tier assignment on vendor mobility outcomes under realistic clustering conditions. Using a replication-based power analysis with a before-after-control-impact (BACI) estimator, the study characterises the design's operating characteristics across 8, 16, 24, and 32 clusters, effect sizes of 3, 5, and 8 percentage points, and 2,000 replications per design cell. The analysis assumes a between-cluster standard deviation of 6.0, a residual standard deviation of 4.5, and an intraclass correlation of 0.64. Results indicate that 54 clusters are required to detect a 5-percentage-point effect at 80% power. The findings establish boundary conditions for RDD application to fee-schedule research and specify the cluster counts at which the design becomes informative.